Electronic grade tantalum nitride has found increasing interest as barrier layer films in microelectronic devices. As the size of integrated circuit devices become increasingly smaller, chemical vapor deposition (CVD) shows a unique advantage over physical vapor deposition (PVD) for device fabrication in terms of excellent step coverage for trench and stack cell structures.
For the CVD processing of tantalum nitride thin films, various precursors have been studied thus far. A liquid precursor is desirable for the ease and reproducibility of precursor delivery. Tantalum halides (TaX.sub.5, X=Br, Cl), A. E. Kaloyeros et al. J. Electrochem. Soc. 1999, 146, p.170-176., K. Hieber, Thin Solid films, 1974, 24, p.157-164., suffer from low volatility and difficulty in delivery due to their solid nature.
Reactions of various tantalum sources containing alkylamide ligands to produce tantalum nitride or carbonitride have been previously disclosed. Fix, et. al., Chemical Vapor Deposition of Vanadium, Niobium and Tantalum Nitride Thin Films, Chem. Mater., Vol. 5, (1993) pp. 614-619, discloses the deposition of non-conductive Ta.sub.3 N.sub.5 films from a solid amide complex Ta(NMe.sub.2).sub.5 with ammonia reactant.
Jun et. al., "Low Temperature Deposition of TaCN Films Using Pentakis(diethylamido) tantalum", Jpn. J. Appl. Phys. , Vol. 37, (1998), pp.L30-L32, discloses low temperature deposition (&lt;400.degree. C.) of TaCN from a single source precursor Ta(NEt.sub.2).sub.5. Cho, et al., "Chemical Vapor Deposition of Tantalum Nitride Films Using Pentakis(diethylamide)tantalum and Ammonia", Mater. Res. Soc. Symp. Proc. 1998, vol. 514, p.531-536, describes the use of unstable Ta(NEt.sub.2).sub.5 with ammonia reactant gas to deposit TaN.
EP 0 869 544 A2 describes the reaction of [(CH.sub.3 CH.sub.2).sub.2 N].sub.3 Ta.dbd.NCH.sub.2 CH.sub.3 with ammonia to form tantalum nitride. Preparation of [(CH.sub.3 CH.sub.2).sub.2 N].sub.3 Ta.dbd.NCH.sub.2 CH.sub.3 requires multi-step synthesis procedures taught by Chiu et al., "Syntheses and Characterization of Organoimido Complexes of Tantalum; Potential Single-Source Precursors to Tantalum Nitride, Polyhedron, Vol. 17, Nos. 13-14, (1998) pp. 2187-2190", or thermal conversion of the related metallacycle compound [(CH.sub.3 CH.sub.2).sub.2 N].sub.3 Ta[.eta..sup.2 --CH.sub.3 CH.sub.2 N.dbd.CH(CH.sub.3)] as reported by Takahashi, Y. et al. Chem. Lett. 1978, p.525-528.
Tsai, et. al., "Metalorganic Chemical Vapor Deposition Of Tantalum Nitride By Tertbutylimidotris(Diethylamido)Tantalum For Advanced Metallization", Appl. Phys. Lett. 67, (8) August 1995, pp. 1128-1130 discloses the use of t-BuN.dbd.Ta(NEt.sub.2).sub.3 in TaN CVD at 600.degree. C. This high temperture process is not compatible with integrated circuit process integration.
Chiu, et. al., "Deposition of Tantalum Nitride Thin Films From Ethylimidotantalum Complex", J. Mat. Sci. Lett, Vol. 11, (1992) pp. 96-98, claimed to have used a liquid mixture of the compounds [(CH.sub.3 CH.sub.2).sub.2 N].sub.3 Ta.dbd.NCH.sub.2 CH.sub.3 and [(CH.sub.3 CH.sub.2).sub.2 N].sub.3 Ta[.eta..sup.2 --CH.sub.3 CH.sub.2 N.dbd.CH(CH.sub.3)]. The films deposited at 500-650.degree. C. without any reactant gas contained a significant amount of carbons.
The problems of the prior art have been overcome by the present invention, by providing an appropriate liquid precursor with an attractive vapor pressure for direct liquid injection chemical vapor deposition of tantalum nitride in a thermal process as will be set forth in greater detail below.